1. Field of the Invention
The present invention relates generally to a cross connect system. In particular, the present invention relates to a switch capacity increasing method which can increase the switch capacity by utilizing the existing switch network as it is.
2. Background of the Related Art
Generally, a 3-stage Clos switch network as shown in FIG. 1 has been widely used in a cross connect system. Referring to FIG. 1, the 3-stage Clos switch network comprises a first stage 10 having a plurality of switching elements 10a–10n, a second stage 20 having a plurality of switching elements 20a–20n connected to the switching elements 10a–10n of the first stage 10 in a many-to-many relationship, and a third stage 30 having a plurality of switching elements 30a–30n connected to the switching elements 20a–20n of the second stage 20 in a many-to-many relationship.
Here, the whole switch capacity N of the switch network is predetermined when the switch network is designed. If the number of input/output of a switching element is defined by n, the ratio of the input number to the output number of each switching element in the first stage 10 becomes n×2n, and the ratio of the input number to the output number of each switching element in the third stage 30 becomes 2n×n.
Also, the ratio of the input number to the output number of each switching element in the second stage 20 becomes N/n×N/n. Accordingly, the first stage 10 and the third stage 30 have a symmetrical arrangement based on the second stage 20.
Such a switch network as described above has the reduced number of cross points and high accessibility of crossbars, and a non-blocking is effected when two terminal points are connected to each other since at least one path is provided through the network to connect the two terminal points together. Because of the above reason, there is a tendency to apply the switch network as shown in FIG. 1, for instance, to the product name DACS IV (digital access communication system IV) manufactured by Lucent in the United States and to the product name 1631SX manufactured by Alcatel in the United States.
In the above-described switch network, the switching elements in the respective stages 10–30 are inserted into a shelf of the cross connect system in the form of a module or unit. On the rear surface of the shelf is provided a mother board in which a plurality of patterns for connecting input/output terminals of the respective modules as designed. Accordingly, the designer of the cross connect system should design or produce the switch network after determining the whole switch capacity of the switch network required at the present time and in the future.
In the conventional cross connect system as shown in FIG. 1, the method of increasing the whole capacity of the switch network may be classified into two.
One method is to produce the switch network having the switch capacity of 2N if the designer judges that the whole switch capacity required at the present time is N, but the switch capacity of 2N will be required thereafter. Another method is to produce and use the switch network having the switch capacity of N, and if required thereafter, to produce a new switch network having the switch capacity of 2N without using the previous switch network having the switch capacity of N any more.
However, the former method has problems that unnecessary expenses are spared on producing the switch network having the switch capacity of 2N though the switch capacity of N is only required at the present time. The latter method also has problems that excessive expenses are spared on producing a new switch network having the switch capacity of 2N since the previous switch network having the switch capacity of N is not used any more.
Such problems are caused by the fixed structure of the produced switch network. Specifically, the fixedly patterned structure of the shelf and the mother board of the cross connect system, which is just like a printed circuit board (PCB), causes the problems in case of increasing the switch capacity of the present switch network.